This invention relates to a process for localisation of defective stations in a local network of stations each provided with error detection- and error reporting means which act in response to station-internal conditions.
Such a local network (FIG. 1) serves for the transmission of information between several stations, which are coupled to one another via a bus.
The communication takes place in the way that information is transmitted bit-serially from the sender stations in coded form and as messages. Depending on the bus concept, there may be one or else several receiver stations, which accept a message and decode the information.
The manner in which the receivers of a message are determined depends essentially on the bus concept (SAE paper 830536). In some systems, the station are provided with station addresses, the addresses of sender and receiver being contained in the messages as a constituent part. A station becomes the receiver of a message if it finds its station address in the message. This means, however, that the user has to know the station addresses of other stations in order to transmit a message.
If several stations are to receive a message, this message must be sent by the sender station several times an appropriate receiver station address in each case. Thus, in such systems, elements of the system configuration must be known and administered on the user level. Other systems do not have station addresses and the associated restricted system flexibility. In the case of these systems, each information item is uniquely marked by an identifier. Each station decides on the basis of the identifier whether it has to accept the message or not. In this case, a message can be received from several stations simultaneously. An example of such a local network is the Controller Area Network (CAN), conceived for use in automobiles (SAE paper 860391).
In order to ensure data integrity in local networks, receiver stations check the correctness of a received message by means of error security processes and report back to the sending station the correct or incorrect reception of the message. Such a check-back report may take place by acknowledgement of the reception in a special acknowledgement sector of the message (FIG. 2). Also, specific bit sequences may be provided as error message and used by each station in the event of an error to break off a transmission of a message in progress which has been detected as erroneous and to arrange that all other stations likewise do not accept the message (FIG. 3).
The capability of stations to break off incorrectly transmitted messages can lead to adverse effects going as far as blockage of the bus if, in an extreme case, all transmitted messages are wrongly declared erroneous by a defective station. In such a situation, due to the defect of one station, none of the other stations would be capable any longer of using the bus for communication purposes.